1. Field of the Invention
The invention relates to a metal catalyst without a carrier for the soot-free production of a fuel gas mixture containing carbon monoxide, hydrogen and gaseous hydrocarbons by partial oxidation of liquid hydrocarbons with air, with air numbers below 0.3 and temperatures between 600 .degree. and 800.degree. C.
2. Discussion of the Prior Art
It has been known for a long time that metal bodies of platinum having a large surface can be used as catalysts for various reactions. For example, U.S. Pat. No. 3,828,736, discloses a process in which a porous body of platinum or nickel such as nickel sponge is heated to an elevated temperature, and the heated catalyst is reacted with a mixture of liquid hydrocarbons and an oxygen-containing gas such as air, exhaust gas or an air/exhaust gas mixture. This process produces a gas mixture which contains hydrogen, carbon monoxide, methane and certain admixtures of low molecular weight hydrocarbons having up to four carbon atoms per molecule. This gas mixture is mixed with more air and burned in an internal-combustion engine connected thereto.
A device for the decomposition of liquid fuels into a propellent in which liquid fuel such as hydrazine or a hydrocarbon, possibly mixed with air, is conducted over a heated porous body of metal foam, is also known.
The gas mixtures generated in these reactions can be used advantageously for the operation of combustion devices such as internal-combustion engines or burners. These gas mixtures are also suitable for generating hydrogen or gas mixtures of a given composition, for example, reducing gases for various technical applications such as metallurgical processes.
The metal catalyst normally employed in these known procedures is either nickel or platinum. However, these known procedures suffer from a number of disadvantages which are related to the catalyst system. For example it is not practical to use platinum catalysts in large scale operations because of their high price. Nickel or nickel-containing metal alloys are not satisfactory because they tend to form soot in the partial oxidation of hydrocarbons under heavy air deficiency. It is known that in gas mixtures which have been generated by oxidation of hydrocarbons with air and low air numbers, part of the carbon is present in the form of soot. The air number is understood to be the ratio of the amount of air actually used to the amount of air which is required for the stoichiometric combustion of the hydrocarbon used. With air numbers below about 0.3, soot is always produced in a reaction which leads up to the thermodynamic equilibrium. Soot precipitation, however, not only leads to disturbances in the operation if the gas mixture produced is used in internal-combustion engines or burners, but the catalysts themselves are contaminated by the soot and their activity is reduced. Therefore, there is a need for a catalyst which furnishes a soot-free gas product with air numbers between about 0.07 and about 0.25. In addition, there is a need for a catalyst which is not deactivated by impurities such as sulfur in in the hydrocarbons used.
A large number of catalysts are known in which metals, usually in the form of metal oxides, are applied as active components on a ceramic carrier. These ceramic carriers usually contain aluminum oxide which may be present in different forms. The thermally unstable forms of the Al.sub.2 O.sub.3 are distinguished by the fact that they themselves already have many active centers due to their crystal structure so that these forms are themselves already catalytically active and, therefore, can effectively aid the activity of the other catalytic components. However, there is a drawback to the use of these carriers because at the operating temperatures of the process these forms of Al.sub.2 O.sub.3 are transformed into .alpha.-Al.sub.2 O.sub.3 which has no appreciable activity. Such catalysts with Al.sub.2 O.sub.3 --containing carriers are, therefore, temperature-sensitive. An additional drawback to the use of such carriers, is that there exists the possibility that the activity of such catalysts will be destroyed if they are subjected to high process temperatures in the presence of excess air, such as in the case of air break-ins, or when the catalyst is shut down.
The carriers of such catalysts must exhibit a highly porous structure in order to provide a sufficiently large surface area. The porous structure results in another drawback because it results in a reduction of thermal conductivity. Good conductivity is advantageous in conducting the process in a safe and reliable manner. Such catalysts also tend to form soot if the fuel is in a liquid form when it strikes the hot catalyst. Therefore, when using the known catalyst having a conventional carrier the liquid fuel must be carefully evaporated or atomized prior to use. This results in an increase in the time and effort required to carry out these processes.
It is therefore an object of this invention to provide a metal catalyst without a carrier for the partial oxidation of liquid hydrocarbons.
It is also an object of this invention to provide a metal catalyst which has high thermal conductivity, and which is extremely stable to thermal and mechanical degradation.
It is still another object of this invention to provide a metal catalyst which maintains a high level of activity over long periods of operation.
It is yet another object of this invention to provide a metal catalyst which is largely insensitive to impurities normally found in hydrocarbon such as sulfur or metals, and which is largely insensitive to air break-ins and contact with liquid fuels.
Still other objects and advantages of the present invention will be obvious and apparent to those of skill in the art from the specification and the appended claims.